1. Field of the Invention
This invention relates to an image stabilizing apparatus capable of correcting a displacement of the image in order to prevent an image deterioration caused by an accidental inclination or a so-called camera shake when a picture is being taken.
2. Description of the Prior Art
When taking a photograph from a moving car or airplane, a taking image tends to displace due to vibration of the moving car or airplane, and particularly where exposure time is long, a fine image is difficult to take. Also, the same problem tends to occur when a long focus lens is used because it is easily adversely affected by vibration.
Means for preventing the displacement of an image caused by such vibration is disclosed in, for example, Japanese Patent Publication No. Sho 57-7416 and Japanese Patent Early Laid-open Publication No. Sho 63-169614.
A liquid prism disclosed in the Japanese Patent Publication No. Sho 57-7416, in which chromatic aberration is corrected, comprises two movable transparent plates disposed with a space between them, a fixed transparent plate disposed between the movable transparent plates for partitioning the space, and two kinds of liquid having different Abbe numbers filled in the respective partitioned spaces. The adjustment of a deflecting function is effected by inclining the movable transparent plates in accordance with the angle of inclination of a lens system.
However, in the liquid prism of the Japanese Patent Publication No. Sho 57-7416, the plural transparent plates must be moved and therefore, the structure becomes complicated. Furthermore, since the outward form of the prism is changed, it is required to have a surplus arrangement space.
Next, the Japanese Patent Early Laid-open Publication No. Sho 63-169614 discloses an apparatus for correcting the displacement of an image by changing the composite deflecting function by pivoting first and second prisms on an optical axis.
However, with the construction of the Japanese Patent Early Laid-open Publication No. Sho 63-169614, the light incident surface of the first prism and outgoing surface of the second prism are not in parallel relation. Accordingly, in case this is to be mounted on a vibration-proof optical system, it is necessary to maintain an arrangement space with reference to the most projected portion and therefore, it also requires a surplus arrangement space.
Also, in the Japanese Patent Early Laid-open Publication No. Sho 63-169614, the angle formed by axes indicating the deflecting function of two prisms is 180.degree. in an initial state as shown in FIG. 24. FIG. 24 shows the deflecting function of the prisms projected onto a plane vertical to the optical axis of the optical system. Therefore, the deflecting function in order to correct the displacement of an image, which is corrected when two prisms are pivoted by a micro angle, is perpendicular to the axes indicating the initial deflecting function. The term "axis of the deflecting function" refers to a vector OP which, as shown in FIG. 25, is drawn from a point of intersection between an optical axis Ax of the optical system and a plane H vertical to the optical axis Ax to a point of intersection between a ray deflected after being made incident to the prism after passing on the optical axis Ax and the plane H. The plane H is, in general, an image plane in an imaging optical system.
FIG. 24 shows a coordinate explaining the deflecting function of the prisms on the image plane, and the origin 0 is a point of intersection between the optical axis of the lens system and the image plane. The amount of deflecting functions of the two prisms are the same.
In the Figure, the deflecting function on the image plane by the first prism in the initial state is expressed by vector A0 and the deflecting function by the second prism is likewise expressed by vector B0. In the initial state, the two vectors form an angle of 180.degree.. Since the two vectors offset each other, the image is not displaced.
In case the first prism is pivoted clockwise or in case the second prism is pivoted counterclockwise, the vectors indicating the deflection function of the respective prisms are expressed by a linear line of which starting point is the origin 0 and terminal point is a point on a circular arc R. In the Figure, the respective circular arcs indicated with angles are used as a coordinate for explaining the vector composed of the deflecting functions of the two prisms. The radius of each reference arc is the same as the vectors A0 and B0, and the centers thereof are points spaced apart by 10.degree. along on the circular arc R.
The reference arc indicated by a plus angle is an aggregation of dots which can be the terminal point of the vector indicating the deflecting function composed when the vector A0 is pivoted by that angle. The reference arc expressed by the same minus angle, is an aggregation of dots which can be the terminal point of the vector composed when the vector B0 is pivoted by the angle. Therefore, if the angles of pivot for the both prisms are apparent, the deflecting function be indicated as the vector drawn from the origin 0 to the point determined by pivot angles.
For example, the deflecting function is indicated by vector C when the first prism (vector A0) is pivoted by 30.degree. from the initial state and the second prism (vector B0) is pivoted by -20.degree..
With the above-mentioned construction, when the direction of the deflecting function needed to correct the image displacement is not coincident with the initial deflecting function A0, B0, the first and second prisms must be instantaneously pivoted normally and reversely by 90.degree.; and there arises a problem in responsibility.
Also, a signal for controlling the pivot of the prisms become a complicated function based on the initial positions of the prisms.